Applications involving mobile equipment sometime require AC power service. Typical mobile applications include recreational vehicles, emergency vehicles such as rescue trucks, ambulances and fire trucks, service repair trucks and small marine vessels such as power boats and sailing boats. AC power service is normally not available in such situations but may be provided on a limited power basis by connecting an inverter to a storage battery or on board generator.
In a certain class of small marine vessels, for example, a prime mover (for example a diesel engine) drives a DC generator for supplying electrical service to DC power loads such as communications equipment and running lights. The prime mover also drives a variable mechanical load, with the principal mechanical load being the propeller, and including auxiliary mechanical loads such as pumps and the like.
An example of a small marine vessel of the foregoing type is an intermediate size sailboat or power boat which is equipped with a small diesel engine and a DC generator. Boats of that class sometime include living accommodations. In such rigs, it is desirable to provide AC power for operating personal convenience equipment such as air conditioners, television sets, hair dryers and microwave ovens, all of which require constant frequency 60 cycle AC power, which is not provided by the onboard DC generator. AC power service for such personal convenience equipment may sometimes be provided by a public utility at the dock, but is usually not otherwise available. Moreover, it may not be practical to connect an inverter to the onboard battery to produce AC operating power for heavy load requirements.
The prime mover engine may be used for generating AC power. However, a complicating factor in producing constant frequency 60 Hz AC power from a variable speed prime mover is that its RPM output is not constant throughout the various boating operations. Additionally, its RPM fluctuates somewhat as auxiliary mechanical loads are connected and disconnected. One further limiting factor in retrofitting a small marine vessel or land vehicle with AC power capability is the limited amount of space available in the engine compartment. In most instances, there is simply not enough space available to accommodate a constant output speed transmission and a conventional 60 Hz alternator which is capable of producing an adequate level of power (for example 3 KVA) required to operate a variety of personal convenience appliances.